1. Field of the Invention
The present invention relates to an electrophotographic copier, optical printer, facsimile apparatus or similar image forming apparatus of the type having a charging member for charging a photoconductive element implemented as a drum or a belt in contact therewith.
2. Discussion of Background
An image forming apparatus of the type described has a charger for charging a photoconductive element. A corona charger, which is specific form of the charger, is extensively used since it can charge the surface of the photoconductive element uniformly. A corona charger, however, produces harmful ozone and nitrogen oxides as a result of corona discharge. Further, such ozone and nitrogen oxides are apt to deposit on the photoconductive element, charger, optics and other constituents of the apparatus, degrading image quality available with the apparatus.
In light of the above, there has been proposed a charging device having a charging member capable of charging the photoconductive element in contact therewith by being applied with a voltage, as taught in, for example, Japanese Patent Laid-Open Publication No. 63-149668. Even such a contact type charging device has some issues yet to be solved, as follows. For example, the device successfully lowers the voltage necessary for the surface of the photoconductive element to be charged to a desired potential and, therefore, enhances efficient charging. However, despite that a cleaning unit cleans the surface of the photoconductive element after the transfer of a toner image from the element to a paper, some toner is still left on the element and transferred to the surface of a charge roller, or charging member, in stripes. The toner so deposited on the charge roller invites defective charging which would result in an irregular charge distribution and defective including blurred images and images with white stripes or black stripes.
To eliminate the above problem, a cleaning m ember implemented by felt may be constantly held in contact with the charge roller in order to clean the surface of the roller, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 2-272582. Alternatively, the cleaning member may be implemented by foam polyurethane, foam polyethylene or similar sponge, as proposed in, for example, Japanese Patent Laid-Open Publication No. 3-101768. Also proposed in the past is a cleaning member movable into and out of contact with the charge roller. A problem with such conventional configurations is that both the cleaning member and the charging member suffer from a lack of durability. Another problem is that when the cleaning member is deteriorated, toner deposits on the charging member is irregular amounts and, therefore, appears in stripes or irregularities in an image.